A significant proportion of the cerebellar cortex receives tactile projections which are organized in a highly precise patchy arrangement termed "fractured somatotopy." In the rat, the preponderance of tactile input, at least of those ares which have been mapped adequately, arises from regions of trigeminal sensory innervation. The trigeminal sensory complex transmits information to the cerebellar cortex via two circuits, the trigeminal mossy fiber - granule cell - Purkinje cell circuit and the trigeminal - olivary climbing fiber - Purkinje cell circuit. Although these two circuits exhibit profound organizational and functional differences, each cerebellar cortical patch receives spatially precise, exquisitely discrete inputs via both circuits. Yet little attention has been directed toward examining the functional differentiation of these two circuits with regard to the information which they convey about the nature of facial cutaneous stimuli. The purpose of the proposed research is to examine quantitatively the stimulus-response relationships within these two different trigeminal circuits which converge upon Purkinje cells of the cerebellar cortex. These studies will employ a comprehensive battery of quantitatively controlled mechanical stimuli applied to the rat's mystacial vibrissae. Single-unit responses will be analyzed by means of a variety of quantitative procedures. We feel that the proposed research, directed toward questions which have been largely ignored, will fill conspicuous and important gaps in our understanding of cerebellar function.